Spark plug with an internal resistor

ABSTRACT

An improved low inductance spring for holding a noise suppression resistor either in the bore of a spark plug insulator or at some other suitable point in the ignition system for an internal combustion engine. The spring is formed from an elongated resilient conductor which is preferably flat. The conductor is shaped to have a plurality of reverse bends which simulate pleats in the bellows of an accordion.

United States Patent Inventor Carl J. Eaton Toledo, Ohio Appl. No. 2,752

Filed Jan. 14, 1970 Patented Sept. 7, 197 1 Assignee Champion Spark Plug Company Toledo, Ohio SPARK PLUG WITH AN INTERNAL RESISTOR 7 Claims, 5 Drawing Figs.

U.S.Cl 313/118, 313/135,3l3/136 Int. Cl H01t13/00 FieldofSearch 313/118, 136,135

[56] Reierences Cited UNITED STATES PATENTS 2,723,364 11/1955 Cipriani et a1. 315/58 3,014,150 12/1961 Szilagyl 313/129 Primary Examiner-Ronald L. \Vibert Assistant Examiner -T. Major Attorney-Owen & Owen ABSTRACT: An improved low inductance spring for holding a noise suppression resistor either in the bore of a spark plug insulator or at some other suitable point in the ignition system for an internal combustion engine. The spring is formed from an elongated resilient conductor which is preferably flat. The conductor is shaped to have a plurality of reverse bends which simulate pleats in the bellows of an accordion.

SPARK PLUG WITH AN INTERNAL RESISTOR BACKGROUND OF THE INVENTION This invention relates to ignition systems for internal combustion engines and more particularly to an improved low inductance spring for positioning a noise suppression resistor in an ignition system.

The use of resistors in the high voltage portion of automotive ignition-systems to suppress undesirable radio frequency emanations is well known in the art. Such resistors are either distributed in the ignition cables or placed at one or more fixed points in the ignition system, for example, in spark plugs, in ignition cable terminals, in the distributor cap, or in the distributor rotor. When a suppression resistor is placed at a fixed point, a spring is usually used to electrically connect one end of the resistor to an adjacent terminal. The spring compensates for the tolerances of the assembled parts and assures good electrical contact under all operating conditions. Prior art springs have been of the spiral coil variety and as such are inductors that form resonant circuits with the capacitance inherent in the ignition system. When excited by spark discharges, this circuit will oscillate and radiate strong radio frequency signals. The values of capacitance and inductance are commonly such that the radiated signals will have a frequency falling within that portion of the frequency spectrum used for radio communication and other related services, thus causing undesirable interference.

SUMMARY OF THE INVENTION According to the instant invention, an improved spring is provided for use in securing a resistor in the bore of a spark plug or in some other suitable location in an ignition system. The spring is capable of performing its resilient mechanical and electrical mounting functions while having a minimum inductance, thus reducing the likelihood that undesirable radio interference will be created. The spring is formed from an elongated piece of resilient conductive material which preferably has a rectangular or flat cross section. The elongated piece of material has a number of reverse folds or bends which are shaped similar to pleats in the bellows of an accordion. The opposed end portions of the compressed spring are parallel for providing a good electrical contact with the suppression resistor and with an adjacent terminal. Since the spring is not coiled, the inductance inherent in the spring will be at a minimum, regardless of the state of compression of the spring. Therefore, the problem of the spring forming a resonant circuit with the capacitance of the ignition system is minimized.

Accordingly, it is a primary object of the invention to provide an improved spring for mounting an interference suppression resistor in an ignition system for an internal combustion engine.

Another object of the invention is to reduce the inductance in the ignition system for an internal combustion engine to reduce the likelihood of generating radio frequency interference.

Other objects and advantages of the invention will become apparent from the following detailed description, reference being made to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially sectioned elevational view of a spark plug including a noise suppression resistor and a spring according to the instant invention;

FIG. 2 is an enlarged cross-sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a front elevational view of a spring according to the instant invention;

FIG. 4 is a side elevational view of a spring according to the instant invention; and

FIG. 5 is an enlarged elevational view showing a spring according to the instant invention and compressed between a spark plug electrode and an interference suppression resistor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIGS. 1 and 2, a spark plug 10 is shown incorporating a spring 11 according to the instant invention. The spark plug 10 generally comprises an outer shell 12 having a threaded lower end 13 for engaging the head'of an internal combustion engine and an insulator 14!. The insulator 14, which is mounted within the shell 12., has an axial bore 15 for mounting a center electrode 16. The center electrode 16 has a firing tip 17 which defines a spark gap with a ground electrode 18, which is attached to the threaded end 13 of the shell 12. The center electrode 16 is electrically connected in series through the spring 1 1 and an interference suppression resistor 19 to an external terminal 20. The resistor 19 may, for exam ple, be either a conventional carbon resistor or a wire wound resistor. The spring 11 forces the resistor 19 against the external terminal 20 to maintain an electrical contact between the resistor 19 and the terminal 20 and to simultaneously maintain an electrical contact between the resistor 19 and the electrode 16. A good electrical contact will be maintained by the spring 11, even though the electrode 16 and the resistor 19 expand and contract as the spark plug 10 is heated and cooled. It will be appreciated that although the spring 11 is shown between the resistor 19 and the center electrode 16, the spring 11 may be similarly positioned between the resistor 19 and the external terminal 20.

Referring now to FIGS. 3-5, the spring 11 is shown in detail. Although the spring 11 may be formed from a resilient wire, it is preferably formed from an elongated resilient piece of conductive material having a generally flat or rectangular cross section, as shown. The spring 11 has two opposed end portions 21 and 22 and a plurality of reverse bends 23 separating a plurality of intermediate side portions 24. The reverse bends 23 and the side portions 24 are shaped similar to pleats in the bellows of an accordion. Although the spring 11 is shown having four reverse bends 23 which form three intermediate side portions 24, it is to be understood that the spring 11 may include either fewer or additional bends 23 to form either fewer or additional side portions 2 1. The bends 23 are preferably spaced to provide uniform side portions 24. As shown in FIG. 4, the side profile of the spring 11, when either compressed or uncompressed, is flat. The flat profile significantly reduces the inductance of the spring 11.

The spring 11 is shown in FIG. 5 compressed between the electrode 16 and the resistor 19. The end 21 of the spring 11 is maintained in substantially flat contact with the electrode 16 while the end 22 is maintained in substantially flat contact with the resistor 19, thereby maintaining a good electrical connection between the electrode 16 and the resistor 19.

Although the spring 11 is shown embodied in a spark plug 10 for an internal combustion engine, it is to be understood that the spring 11 may be used for mounting resistors in other locations in the ignition system for an internal combustion engine. It has been found, for example, that an interference suppression resistor may be mounted in the distributor rotor or cap for an internal combustion engine. A resistor-receiving bore is formed in the rotor or cap and one end of the resistor is positioned against a terminal. The spring 11 is then used to connect the other end of the resistor to a second terminal. The spring 11 may be similarly used for mounting an interference suppression resistor in a terminal for connecting an ignition cable to a spark plug. In each of these cases, the spring 11 significantly reduces the inductance of the ignition system over a system in which a conventional spiral spring is used for mounting an interference suppression resistor.

What I claim is:

- 1. In a spark plug for an internal combustion engine having an insulator surrounding a center electrode, said electrode being connected to an external terminal by a resistor positionedwithin the bore of said insulator, a low inductance spring for maintaining electrical contact between said resistor, said electrode and said terminal, said spring comprising an elongated resilient conductor, said conductor having a plurality of reverse bends longitudinally spaced therealong and having a maximum compressed width less than the diameter of the bore of said insulator, said spring being positioned in the bore of said insulator and compressed between said resistor and one of said electrode and said terminal.

2. An improved spark plug for an internal combustion engine, as claimed in claim 1, wherein said spring is formed from a flat elongated conductor.

3. An improved spark plug for an internal combustion engine, as claimed in claim 2, wherein one end of said spring is formed to maintain flat contact with an end of said resistor and the other end of said spring is formed to maintain flat contact with an end of one of said electrode and said terminal.

4. An improved spark plug for an internal combustion engine, as claimed in claim 2, wherein said reverse bends are substantially uniform and are uniformly spaced along said conductor to resemble accordion pleats.

5. In an ignition system for an internal combustion engine including a radio interference suppression resistor, an improved low inductance spring for electrically connecting said resistor to a terminal, said spring comprising an elongated resilient conductor, said conductor having a plurality of reverse bends longitudinally spaced therealong to resemble accordion pleats, said spring being compressed between said resistor and said terminal, and the end portions of said spring being formed to maintain flat contact with said resistor and said terminal.

6. A low inductance spring for connecting a suppression resistor in an ignition system for an internal combustion engine, as defined in claim 5, wherein said spring is formed from a flat elongated conductor.

7. A low inductance spring for connecting a suppression resistor in an ignition system for an internal combustion engine, as defined in claim 5, wherein said reverse bends are substantially uniform and are spaced along said conductor. 

1. In a spark plug for an internal combustion engine having an insulator surrounding a center electrode, said electrode being connected to an external terminal by a resistor positioned within the bore of said insulator, a low inductance spring for maintaining electrical contact between said resistor, said electrode and said terminal, said spring comprising an elongated resilient conductor, said conductor having a plurality of reverse bends longitudinally spaced therealong and having a maximum compressed width less than the diameter of the bore of said insulator, said spring being positioned in the bore of said insulator and compressed between said resistor and one of said electrode and said terminal.
 2. An improved spark plug for an internal combustion engine, as claimed in claim 1, wherein said spring is formed from a flat elongated conductor.
 3. An improved spark plug for an internal combustion engine, as claimed in claim 2, wherein one end of said spring is formed to maintain flat contact with an end of said resistor and the other end of said spring is formed to maintain flat contact with an end of one of said electrode and said terminal.
 4. An improved spark plug for an internal combustion engine, as claimed in claim 2, wherein said reverse bends are substantially uniform and are uniformly spaced along said conductor to resemble accordion pleats.
 5. In an ignition system for an internal combustion engine including a radio interference suppression resistor, an improved low inductance spring for electrically connecting said resistor to a terminal, said spring comprising an elongated resilient conductor, said conductor having a plurality of reverse bends longitudinally spaced therealong to resemble accordion pleats, said spring being compressed between said resistor and said terminal, and the end portions of said spring being formed to maintain flat contact with said resistor and said terminal.
 6. A low inductance spring for connecting a suppression resistor in an ignition system for an internal combustion engine, as defined in claim 5, wherein said spring is formed from a flat elongated conductor.
 7. A low inductance spring for connecting a suppression resistor in an ignition system for an internal combustion engine, as defined in claim 5, wherein said reverse bends are substantially uniform and are spaced along said conductor. 